The present invention relates to a flame-retardant thermotropic polyester composition having superior flame retardancy, excellent mechanical properties and great heat resistance, and to a shaped article of excellent appearance, molded from the composition.
The demand for an enhancement of the performances of plastics has recently increased, so many polymers having various novel performances have been developed and marketed. Among these polymers, optically anisotropic liquid crystal polymers characterized by parallel configuration of molecular chains have attracted attention, due to their superior flowability and mechanical properties, and the application of these polymers as machine parts, electric and electronic parts, and the like is widening.
In addition to the balance among general chemical and physical properties, a high degree of safety against flame, i.e., intense flame retardancy, is required for these industrial materials.
It is known, in general, that liquid crystal polymers have combustion resistance and when such polymers are directly exposed to flame, spontaneously occurring foam generates a carbonized layer.
Nevertheless, it was found that since a liquid crystal polyester as one of the representative liquid crystal polymer, formed by copolymerizing a polyester derived from an alkylene glycol and a dicarboxylic acid with an acyloxy aromatic carboxylic acid (for example, a polymer disclosed in U.S. Pat. No. 3,778,410/1973) did not have sufficient flame retardancy when the polyester was made into a thin (1/32") shaped article. It is known that such liquid crystal polyester acquires flame retardancy with the combined use of organic bromine compound and antimony compound (Japanese Patent Laid-open No. 118567/1988). It was found, however, that the addition of a vast amount of such compounds was inevitable, resulting in extremely poor retention stability at molding.
Thus, the present inventors found that the liquid crystal polyester of a specified structure could get flame retardancy with the use of a minor amount of organic bromine compounds alone, without the use of antimony compounds in combination, and that the retention stability thereof at molding remarkably could be enhanced.
However, it was found that even when the polyester was retained for a long time at high temperatures of 300.degree. C. or more, the organic bromine compounds decomposed, leading to the degradation of the liquid crystal polyester. It was also found that the flame retardancy of its thin shaped article of a thickness of 1/32" or less was not always satisfactory.